Galaxies

So far we have seen the Universe evolve
from a tiny point of false vacuum into a huge dark gas of simple atoms 380
million years later. The next big step in history was the formation of the
first stars and galaxies.

A galaxy is an island of stars, typically hundreds of billions of them, separated from hundreds of billions of other galaxies by a
vast ocean of almost empty space. In this story we will look at one particular
galaxy (the Milky
Way), since that is the one we know best,
the one where we live. But we should not forget that, scattered far and wide
across the Universe,
there are hundreds of billions of other galaxies very similar to ours. So
before we focus down on the galaxy where we live, let's first look at the big
picture.